Lumbar spinal stenosis (“LSS”), and sometimes called sciatica) is a condition of the spine characterized by a narrowing of the lumbar spinal canal. With spinal stenosis, the spinal canal narrows and pinches the spinal cord and nerves, causing pain in the back and legs. It is estimated that approximately 5 in 10,000 people develop LSS each year. For patients who seek the aid of a physician specialist for back pain, approximately 12-15% are diagnosed as having LSS.
Several causes of spinal stenosis have been identified, including aging, heredity, arthritis, and changes in blood flow to the lower spine. Aging is believed to be the most common cause, because as a person ages the ligaments connecting the bones of the spine can thicken and spurs may develop on the bones and into the spinal canal. The cushioning discs between the vertebrae also frequently deteriorate, and the facet joints may begin to break down. Heredity is believed to play a role in some cases because it may cause some people to have a smaller than average spinal canal, typically leading to LSS symptoms even at a relatively young age.
The most common symptoms of spinal stenosis are pain and difficulty when walking, although numbness, tingling, hot or cold feelings in the legs, and weakness or tiredness may also be experienced. In extreme cases spinal stenosis can cause cauda equina syndrome, a syndrome characterized by neuromuscular dysfunction that may result in permanent nerve damage.
Common treatments for LSS include physical therapy (including changes in posture), medication, and occasionally surgery. Changes in posture and physical therapy may be effective in flexing the spine to enlarge the space available to the spinal cord and nerves—thus relieving pressure on pinched nerves. Medications such as NSAIDS and other anti-inflammatory medications are often used to alleviate pain, although they are not typically effective at addressing the cause of the pain. Surgical treatments are more aggressive than medication or physical therapy, but in appropriate cases surgery may be the best way to achieve a lessening of the symptoms associated with LSS.
The most common surgery for treating LSS is decompressive laminectomy, in which the lamina of one or more vertebrae is removed to create more space for the nerves. The intervertebral disc may also be removed, and the vertebrae may be fused to strengthen unstable segments. The success rate of decompressive laminectomy has been reported to be in excess of 65%, with a significant reduction in LSS symptoms being achieved in many cases.
More recently, a second surgical technique has been developed in which the vertebrae are distracted and an interspinous spacer is implanted to maintain the desired separation between the segments. This technique is somewhat less invasive than decompressive laminectomy, but may provide significant benefits to patients experiencing LSS symptoms.
As with other surgeries, one consideration when performing surgery to implant an interspinous spacer is the size of the incision that is required to allow introduction of the device. Minimally invasive techniques are generally preferred, but the interspinous spacers previously known to the art did not work well with minimally invasive surgical techniques. The implantation profile presented by known spacers precludes introduction through a very small incision.
A need therefore exists for an interspinous spacer that can be implanted using minimally invasive surgical techniques. The present invention addresses that need.